(a) Field of the Invention
The present invention relates to a hybrid vehicle. More particularly, the present invention relates to a system and a method for idle charge of a hybrid vehicle that changes an entering point and a releasing point of idle charge control considering entering times to the idle charge control according to a driving condition.
(b) Description of the Related Art
The hybrid vehicle is provided with an engine such as a gasoline engine or a diesel engine and a motor (motor/generator) generating electricity by using engine output and driven by electricity stored in a battery so as to assist the engine output.
The hybrid vehicle improves fuel economy by using the motor as a main power source or an auxiliary power source at a region where engine efficiency is low, and by generating the electricity through regenerative braking and storing it in the battery during deceleration.
Whether the engine is started or stopped and distribution of torque to the engine and the motor has great influence on fuel economy and drivability of the hybrid vehicle.
Whether the engine is started or stopped and the distribution of the torque to the engine and the motor is determined by various factors including vehicle speed, displacement of an accelerator pedal, and shift speed. The most important factor among them is an SOC (State Of Charge) of a battery.
A method for managing the SOC of the battery is idle charge control in which the engine is started and the motor is operated as the generator so as to raise the SOC of the battery when the SOC of the battery is lowered under a predetermined voltage.
In addition, the SOC of the battery may be maintained at an optimal state by performing the idle charge control efficiently.
According to an idle charge control applied to a conventional hybrid vehicle, SOC value (%) for entering the idle charge control and SOC value (%) for being released from the idle charge control are constant.
For example, the SOC value for entering the idle charge control may be fixedly set as 50% of battery charge, and the SOC value for being released from the idle charge control may be fixedly set as 55% of battery charge.
Therefore, the engine is forcibly started and the idle charge control is performed in a case that the SOC of the battery decreases lower than 50% of the battery charge, and the idle charge control is released in a case that the SOC of the battery increases higher than 55% of the battery charge as the idle charge control is performed.
If the SOC value for entering or being released from the idle charge control is constant, the engine may be started or stopped frequently when the hybrid vehicle runs in congested areas only with the motor (EV mode).
Therefore, a driver may feel a sense of incompatibility and marketability may be deteriorated.
In order to prevent a frequent switch of engine operation, idle charge control region may be enlarged.
For example, the SOC value for entering the idle charge control may be fixedly set as 40% of the battery charge, and the SOC value for being released from the idle charge control may be fixedly set as 70% of the battery charge.
However, a simple enlargement of the idle charge control region may cause unequal distribution of torque to the engine and the motor. Therefore, fuel economy may be deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form prior art and/or that is not already known in this country to a person of ordinary skill in the art.